Physiologic principles and adaptations form the basis for marathon training requirements. There are two basic principles which underlie all types of athletic training: overload and specificity.
Overload means exercising at a level which causes the body to make specific adaptations to function more efficiently. Overload does not mean overtraining. Think of a rubberband - as more pull is applied it stretches more and becomes easier to stretch, but too much pull can cause it to snap. To keep the runner from breaking, i.e., becoming injured or ill, overload must always be used in conjunction with rest. Overload and rest form the basis for what is known as the "hard/easy" training approach. This technique uses variations in frequency, intensity and duration to achieve cycles of overload and rest. Frequency is how often you run, intensity is the pace at which the workout is conducted and duration is the time spent on an individual run. In a program of increasing mileage or of building basic endurance, "hard" may be a long slow run while "easy" may be a shorter distance run at the same effort. For the experienced runner with an established mileage base, "hard" might be a shorter workout of increased intensity such as hill work, fartlek or some kind of interval training. After a hard workout, rest or an easy workout is important because it allows the muscles and other tissues a chance to rebuild and adapt to the stress. This is the basis of overload training.
Specificity refers to adaptations of both metabolic and physiologic systems, depending on the type of overload used. Specific exercise brings about changes in those systems used in that particular exercise. Running is obviously the specific training for running. Different adaptations result from different kinds of running using variations of frequency, intensity, duration and terrain to utilize different sources of energy. This is where long term goal setting is so important: you need a running program designed for the specific type of races you want to run. This approach will assist you to maximize performance and eliminate wasted effort. Specific endurance training with its resultant physiologic adaptations is essential for marathons.
Energy to perform work comes from the generation of a substance called ATP, (adenosine triphosphate). The breakdown of the food provides the sources of this energy. The main energy sources used in endurance running are carbohydrates, (stored in the body as glycogen), and fat. When these materials are broken down in the presence of oxygen, the metabolism or energy used is termed aerobic. The waste products of this aerobic metabolism are water (H20) and carbon dioxide (CO2). Metabolism is termed anaerobic when the glycogen is broken down to form pyruvate and, lacking oxygen, further breaks down into lactic acid.
The body can endure only limited amounts of lactic acid. If lactic acid accumulates, fatigue occurs faster and glycogen breaks down rapidly, depleting your energy source. Anaerobic metabolism provides energy for short intense exercise such as sprinting or for bursts of speed in sports like soccer and basketball. In prolonged exercise, the major metabolic pathway used is the aerobic one. When aerobic metabolism cannot meet the requirements for energy due to either increased intensity or prolonged time, anaerobic metabolism may be called in for short term assistance.
Carbohydrates are the most readily available source of energy in the muscle and are utilized mainly in faster continuous running, especially for shorter distances. Fat is the major supplier of energy at slower paces or for longer distances. More oxygen is required to produce an equal amount of energy when fat rather than glycogen is used as the energy source. In addition fat requires some breakdown of carbohydrates to be taking place simultaneously. The body can not accumulate adequate glycogen stores to provide enough energy for the duration of the marathon. Many marathoners have experienced a severe energy loss around the 20 mile point in a marathon. The effect is referred to affectionately as "Hitting the Wall". Hitting the wall is thought to be the depletion of muscle glycogen. Fat stores (even in the leanest runners) are almost inexhaustible. However, when muscle glycogen is gone, fat is probably unable to be used because it needs some carbohydrate as a primer for its metabolism.
Running the marathon requires a combination of both carbohydrate and fat metabolism. The physiologic goals of a marathon training program are to provide enough endurance training to optimize aerobic metabolism; to have the ability to metabolize fat while running faster paces and to facilitate increased storage of carbohydrates.
These goals require adaptations to allow greater consumption and utilization of oxygen. Some of these changes occur at the local muscle level and include better utilization of oxygen through increased size and number of mitochondria (little energy factories within the cells) and an increase in their aerobic enzymes. These muscles can more easily mobilize and use fat for energy, which helps to preserve the carbohydrate stores. The body also develops a greater ability to store and utilize carbohydrates. Some muscle fibers can be adapted for aerobic or anaerobic metabolism exercise. For the marathon, you want to adapt these convertible muscles for aerobic or endurance work. Through training there will be an increase in the number of capillaries for better nutrient supply as well as an increase in the amount of muscle tissue.
Adaptations of the cardiovascular and respiratory systems are also important results of training. The heart muscle increase in size, weight and the amount of blood increases. Resting and submaximal exercise heart rates are decreased. The amount of blood that the heart pumps, called the stroke volume, increases which aids in increasing the amount of oxygen that can be extracted from the blood through better distribution of blood to the working muscles. As the blood goes through the muscles, increased utilization of oxygen from the blood results in increased consumption of oxygen.
One of the most important training adaptations is an increase in the maximal oxygen uptake, called VO2 Max, which is a quantitative measure of a person"s capacity for aerobic energy transfer (the ability to do work). An improvement in VO2 Max thus increases the amount of work you can do, that is you can run faster and/or farther. Variables that determine VO2 Max are heredity, sex, body composition (the amount of lean body tissue), age and training. Obviously you can do nothing about several of these variables, but improvements of 20-25% in maximal oxygen uptake because of training have been observed. VO2 max peaks within 6 months to 2 years after starting an endurance training program. However, even after it has levelled off, it is still possible to improve performance. Typical marathoners are able to maintain their pace using approximately 75-80% of VO2 Max for the well over 2 hours required. Some athletes, notably ultramarathoners, are able to work for prolonged periods at levels approaching 90% of VO2 Max. The ability to run at higher percentages of VO2 Max may be explained by the concept of anaerobic threshold. Anaerobic threshold is the point when increasing intensity of exercise causes lactic acid to accumulate and impair performance. Improving the anaerobic threshold means that you can run harder for a longer period of time without going into anaerobic metabolism and accumulating much lactic acid. Studies have shown that anaerobic threshold can be increased by endurance training.
Run The Planet thanks Patti & Warren Finke and Team Oregon for the permission to reprint the complete online version of the first edition of the book Marathoning Start to Finish (Hypertext Version 1.02) by Patti & Warren Finke. © 1986, 1996 wY'east Consulting, All Rights reserved.
